A typical landing gear comprises a main strut having an upper portion adapted to be connected to the underside of the aircraft and a lower portion telescoping within the upper portion and pivotally connected to a bogie. The bogie comprises a bogie beam with axles and wheels mounted on the bogie beam fore and aft of a main pivot by which the bogie beam is connected to the lower portion of the main strut.
The main strut can be moved between a deployed position, for ground manoeuvring take off and landing, and a stowed position, for flight. When in the stowed position both the strut and bogie are contained within a landing gear cavity in the aircraft. The bogie beam must be within a range of angular positions with respect to the strut to enable the landing gear to be stowed in the cavity without striking the aircraft fuselage. The angular position or “pitch” of the bogie beam relative to the strut required for stowing is known in the art as its “trimmed” position.
A “pitch trimming” actuator is provided to control the pitch of the bogie beam. A pitch trimming actuator is generally controlled by hydraulic fluid supplied at positive pressure so as to cause the pitch trimming actuator to adopt a predetermined length corresponding to the trimmed position of the bogie beam.
The pitch of the bogie beam can be changed by external forces applied to it, such as when the aircraft lands and during taxiing of the aircraft. The hydraulic fluid supply constantly works against such forces, such that in the absence of any applied forces that exceed the positioning force due to the hydraulic fluid supply, the bogie beam adopts its trimmed position. An example of this is when the aircraft takes off. When taxiing, the pitch trimmer provides a hydraulic damping function that damps pivoting movements of the bogie as it engages bumps or dips in the runway. The applicant has identified that this can lead to deterioration of components of the pitch trimmer and other parts of the landing gear, such as the linkage bearings.